Studies are being conducted to elucidate the cytopathomechanism of radiation cataractogenesis. Previous work indicated that radiation exerts a direct effect upon the lens epithelium, the cells of which undergo aberrant differentiation leading to the development of posterior subcapsular cytoarchitectural changes. Since the germinative zone and the meridional rows have been implicated as the likely site of the initial lesions, investigations will focus on the changes in these areas with particular emphasis on the meridional rows. Upon exposure to cataractogenic doses of X-rays the cells of the meridional rows suffer what has been described classically as interphase death. The number of injured cells is both age and dose dependent and the phenomenon appears ubiquitous among those species susceptible to radiation cataract development. The possible contribution of this early phenomemon to the overall cytoarchitectural changes which precede, and are associated with, the development of cataracts is currently being studied. Of particular interest is the basis of the lesion, an elucidation of which will require a determination of the actual site of injury within the individual cells involved. The work will necessitate monitoring the cell population to determine changes in morphology and ultrastructure as well as macromolecular synthetic events.